Process for cracking synthetic crude oil-containing feedstock

ABSTRACT

A process for steam cracking liquid hydrocarbon feedstocks containing synthetic crude oil comprises i) hydroprocessing a wide boiling range aliquot containing a) normally liquid hydrocarbon portion substantially free of resids and b) thermally cracked hydrocarbon liquid, boiling in a range from about 600° to about 1050° F., to provide a synthetic crude oil substantially free of resids; ii) adding to the synthetic crude oil a normally liquid hydrocarbon component boiling in a range from about 100° to about 1050° F.; and iii) cracking the mixture resulting from ii) in a cracker furnace comprising a radiant coil outlet to provide a cracked effluent, wherein the cracking is carried out under conditions sufficient to effect a radiant coil outlet temperature which is greater than the optimum radiant coil outlet temperature for cracking the synthetic crude oil separately. A method for upgrading synthetic crude for use in cracking is also provided, as well as a feedstock for cracking.

FIELD

The present invention is directed to a method for processing the gaseouseffluent from hydrocarbon pyrolysis units that can use heavy feeds,e.g., synthetic crude oil-containing feeds, as well as a method toupgrade synthetic crude oils.

BACKGROUND

Steam cracking, also referred to as pyrolysis, has long been used tocrack various hydrocarbon feedstocks into olefins, preferably lightolefins such as ethylene, propylene, and butenes. Conventional steamcracking utilizes a pyrolysis furnace which has two main sections: aconvection section and a radiant section. The hydrocarbon feedstocktypically enters the convection section of the furnace as a liquid(except for light feedstocks which enter as a vapor) wherein it istypically heated and vaporized by indirect contact with hot flue gasfrom the radiant section and by direct contact with steam. The vaporizedfeedstock and steam mixture is then introduced into the radiant sectionwhere the cracking takes place. The resulting products, includingolefins, leave the pyrolysis furnace for further downstream processing,including quenching.

Historically, quenching effluent from a heavy feed cracking furnace hasbeen technically challenging. Most modern heavy feed furnaces employ atwo-stage quench, the first stage being a high pressure 10400 to 13900kPa (1500-2000 psig) steam generator and the second stage utilizingdirect oil quench injection. See, e.g., U.S. Pat. No. 3,647,907 to Satoet al., incorporated herein by reference. In the 1960s high pressuresteam generating cracked gas coolers deployed as transfer lineexchangers were found to be especially useful in cracking liquid feeds.The high steam pressure (8100 to 12200 kPa (80 to 120 bar)) and hightube wall temperatures (300° to 350° C.) limited the condensation ofheavy hydrocarbons and attendant coke formation on tube surfaces.

Conventional steam cracking systems have been effective for crackinghigh-quality feedstocks such as gas oil and naphtha. However, steamcracking economics sometimes favor cracking low cost heavy feedstocksuch as, by way of non-limiting examples, crude oil and atmosphericresid, also known as atmospheric pipestill bottoms. Crude oil andatmospheric resid contain high molecular weight, non-volatile componentswith boiling points in excess of 590° C. (1100° F.). The non-volatile,heavy ends of these feedstocks lay down as coke in the convectionsection of conventional pyrolysis furnaces. Only very low levels ofnon-volatiles can be tolerated in the convection section downstream ofthe point where the lighter components have fully vaporized.Additionally, some naphthas are contaminated with crude oil duringtransport. Conventional pyrolysis furnaces do not have the flexibilityto process resids, crudes, or many resid or crude contaminated gas oilsor naphthas, which contain a large fraction of heavy non-volatilehydrocarbons.

Synthetic crude oils are wide boiling range hydrocarbon feeds thatcontain minimal amounts of non-volatile materials. Given the substantialabsence of non-volatiles, e.g., resids (including asphaltenes), fromsynthetic crudes, they appear particularly suitable as feeds forcracking processes. However, conventional synthetic crudes that arehydrotreated blends of non resid containing virgin liquids fromatmospheric or vacuum pipestills, combined with thermally crackedproducts, may exhibit difficulties in cracker operability. Suchdifficulties include low coil outlet temperatures, low conversion andhigh coking in the radiant and quench sections of pyrolysis furnaces.

U.S. Pat. No. 4,176,045 to Leftin et al., which is incorporated hereinby reference, discloses production of C₂ to C₅ olefins by “steampyrolysis, i.e., cracking” of normally liquid hydrocarbons whileminimizing coke deposits on the interior surface of the furnace. Morehighly aromatic, higher coking petroleum derived feedstocks are blendedwith lower coking petroleum derived feedstocks to provide crackingfeedstock.

Leftin, et al., “High-Severity Pyrolysis of Shale and Petroleum Gas OilMixtures,” Ind. Eng. Chem., Process Des. Dev., Vol. 25, No. 1, pp.211-16, January, 1986, teach high-severity pyrolysis of narrow boilingrange shale gas oil and petroleum-derived light gas oil mixtures toreduce coking rates as compared to shale gas oil alone as an alternativeto hydrotreating shale gas oil prior to pyrolysis.

US 2005/0258073 to Oballa et al. discloses that “[a]naromatics/naphthalene rich stream obtained by processing heavy gas oilderived from tar sands and cycle oils derived from cracking heavy gasoil may optionally be blended and subjected to a hydrogenation processand a ring opening reaction” in the presence of a catalyst “to produceparaffinic feedstocks for further chemical processing.”

Sharypov, V. I., et al., Fuel, Vol. 75, No. 7, pp. 791-94, disclosessteam cracking coal-derived liquids with b.p.<350° C.

Gamidov, et al., “Pyrolysis of Coal-Derived Naphtha,” Azerb. Neftr.Khoz., (5) 37-40 (1989) Chem. Abstr. ABSTR. NO. 39538 V112 N6, teachessteam cracking a coal-derived hydrorefined naphtha provides reducedgaseous product yield (7-20%) than that of a straight-run petroleumnaphtha, with the difference widening as severity of the processdecreases. Ethylene yields were 3 to 7% higher for coal-derived naphthaunder “medium high-severity conditions.”

When using synthetic crude oils as a feedstock to a cracker, it would bedesirable to upgrade such feedstocks to improve cracker operability.Such improved feedstocks should provide higher coil outlet temperatures,higher conversion and reduced coking in the radiant and quench sectionsof pyrolysis furnaces.

SUMMARY

In one aspect, the present invention relates to a process for cracking asynthetic crude oil-containing feedstock comprising: i) hydroprocessinga wide boiling range aliquot containing a) normally liquid hydrocarbonportion boiling in a range from about 50° to about 800° F.,substantially free of resids, and b) thermally cracked hydrocarbonliquid boiling in a range from about 600° to about 1050° F., to providea synthetic crude oil boiling in a range of from about 73° to about1070° F., containing greater than about 25 wt % aromatics, greater thanabout 25 wt % naphthenes, less than about 0.3 wt % S, less than about0.02 wt % asphaltenes, and substantially free of resids other thanasphaltenes; ii) adding to the synthetic crude oil a normally liquidhydrocarbon component boiling in a range from about 100° to about 1050°F.; and iii) cracking the mixture resulting from ii) in a crackerfurnace comprising a radiant coil outlet to provide a cracked effluent,wherein the cracking is carried out under conditions sufficient toeffect a radiant coil outlet temperature which is greater than theoptimum radiant coil outlet temperature for cracking the synthetic crudeoil separately.

In certain embodiments of this aspect, the normally liquid hydrocarboncomponent has a greater optimum radiant coil outlet temperature than thesynthetic crude oil. Typically, the normally liquid hydrocarboncomponent is added to the synthetic crude oil in an amount sufficient toincrease at least one of A) cracked effluent temperature at the coiloutlet by from about 5° to about 150° F., say, from about 50° to about70° F., e.g., from about 100° to about 125° F., and B) olefin yieldsresulting from the cracking, as compared to the synthetic crude oilalone.

Embodiments of this aspect can include those wherein the normally liquidhydrocarbon component is selected from the group consisting of lightvirgin naphtha, condensate, kerosene, distillate, heavy atmospheric gasoil, virgin gas oil, hydrotreated gofinate, and hydrocrackate.Typically, the normally liquid hydrocarbon component is selected fromthe group consisting of light virgin naphtha and gas oil. Alternately,the normally liquid hydrocarbon component is selected from the groupconsisting of hydrotreated light virgin naphtha and hydrotreated gasoil.

In certain embodiments of this aspect of the present invention, thesynthetic crude oil has a pour point no greater than about 80° F.,typically no greater than about 70° F., e.g., no greater than about 52°F., say, about −12° F., while the normally liquid hydrocarbon componenthas a pour point greater than about 50° F., say, greater than about 102°F., e.g., greater than about 120° F., and the mixture resulting from ii)has a pour point no greater than about 100° F., say, no greater thanabout 90° F., e.g., no greater than about 80° F.

Embodiments of this aspect of the invention can comprise the processwherein the mixture comprises from about 1 to about 99 wt % normallyliquid hydrocarbon component and from about 1 to about 99 wt % syntheticcrude oil, typically from about 50 to about 80 wt % normally liquidhydrocarbon component and from about 20 to about 50 wt % synthetic crudeoil, e.g., about 75 wt % hydrocrackate and 25 wt % synthetic crude oil.

In one embodiment of this aspect, the normally liquid hydrocarboncomponent is added to the synthetic crude oil in an amount sufficient toreduce the pour point of the mixture resulting from ii). The pour pointcan be reduced by at least about 5° F., typically at least about 10° F.

Certain embodiments of this aspect of the invention include thosewherein the normally liquid hydrocarbon portion is a virgin refineryfeed selected from the group consisting of light virgin naphtha,condensate, kerosene, distillate, heavy atmospheric gas oil, and vacuumgas oil, and the thermally cracked hydrocarbon liquid is selected fromthe group consisting of thermally cracked very heavy crude and coker gasoil.

Other embodiments of this aspect include those wherein the normallyliquid hydrocarbon portion is a hydrotreated refinery stream selectedfrom the group consisting of gofinate and hydrocrackate, and thethermally cracked hydrocarbon liquid is selected from the groupconsisting of thermally cracked very heavy crude and coker gas oil.

In another embodiment, the normally liquid hydrocarbon portion compriseslight virgin napththa condensate, and the thermally cracked hydrocarbonliquid comprises thermally cracked very heavy crude.

Certain embodiments of this aspect of the invention include thosewherein the hydroprocessing is selected from hydrotreating,hydrogenating and hydrocracking.

Additional embodiments of this aspect of the invention include thosewherein the synthetic crude oil contains no greater than about 0.1 wt %S, e.g., no greater than about 0.05 wt % S.

In still other embodiments of this aspect, the normally liquidhydrocarbon component is added to the synthetic crude oil in an amountsufficient to provide an optimum coil outlet temperature of the crackerfurnace for the resulting mixture which is increased by at least about10° F., typically at least about 30° F., e.g., at least about 70° F.,over the optimum coil outlet temperature of the cracker furnace forsynthetic crude oil alone.

In another embodiment of this aspect of the invention, the normallyliquid hydrocarbon component is added to the synthetic crude oil in anamount sufficient to increase the hot cracked effluent temperature atthe coil outlet of the cracker furnace to the optimum coil outlettemperature for the normally liquid hydrocarbon component. Typically,the normally liquid hydrocarbon component is added to the syntheticcrude oil in an amount sufficient to increase severity by at least about0.05 C3=/C1 for each 5° F. increase in coil outlet temperature., e.g.,in an amount sufficient to increase severity by at least about 0.03C3=/C1 for each 5° F. increase in coil outlet temperature.

In still another embodiment of this aspect, the normally liquidhydrocarbon component is added to the synthetic crude oil in an amountsufficient to reduce coke make, by at least about 1 wt %, typically atleast about 10 wt %, e.g., up to about 20 wt %.

In another embodiment of this aspect of the invention, the normallyliquid hydrocarbon component is added to the synthetic crude oil in anamount sufficient to increase olefin yields from cracking by at leastabout 0.1 wt % ethylene, typically at least about 1 wt % ethylene, e.g.,at least about 2 wt % ethylene.

In yet another embodiment of this aspect of the present invention, thenormally liquid hydrocarbon component is added to the synthetic crudeoil to increase the optimum coil outlet temperature (COT) by at leastabout 10° F., typically by at least about 70° F. For present purposes,the term “optimum coil outlet temperature” is defined as the maximumtemperature at which an acceptable rate of radiant or quench cokeformation is effected, except for pentane insoluble-containing feedswherein an acceptable rate of coke formation is effected in theconvection section. Typically, the optimum coil outlet temperature isthat which provides a commercially acceptable runlength for the unit,and can be readily determined by those of skill in the art. Optimum coiloutlet temperature can be determined by tube metal temperature increaserate. For example, a tube metal temperature increase of 125° F. isobserved in a lab unit operating on 75 wt % hydrocrackate and 25 wt %syncrude. Factors affecting the optimum COT include furnace coking anddownstream constraints. Generally, the optimum COT to make more ethylene(whose output peaks at much higher COT than propylene) is to raise COTpast the temperature at which propylene production increases, to makemore methane, more ethylene and less propylene. Coil outlet temperatureis generally maintained below the point where ethylene make peaks.

In certain embodiments of this aspect of the invention, the mixtureresulting from adding the normally liquid hydrocarbon component to thesynthetic crude oil ranges from about 0.1 to about 99 parts by weight,typically from about 1 to about 9 parts by weight, e.g., from about 1 toabout 3 parts by weight of normally liquid hydrocarbon component to eachpart by weight of synthetic crude oil.

In still other embodiments of this aspect, the wide boiling rangealiquot contains from about 0.1 to about 10 parts by weight, typicallyfrom about 2 to about 3 parts by weight of the normally liquidhydrocarbon portion for each part by weight of the thermally crackedhydrocarbon liquid.

In another embodiment of this aspect of the invention, the cracking issteam cracking.

In yet another embodiment of this aspect, the synthetic crude oil isderived from shale and the normally liquid hydrocarbon component isderived from petroleum.

In another aspect, the present invention relates to a process forupgrading synthetic crude oil for cracking which synthetic crude oil isa hydroprocessed mixture of a) normally liquid hydrocarbon portionboiling in a range from about 50° to about 800° F., substantially freeof resids, and b) thermally cracked hydrocarbon liquid boiling in arange from about 600° to about 1050° F., the synthetic crude oil boilingin a range of from about 73° to about 1077° F., containing greater thanabout 25 wt % aromatics, greater than about 25 wt % naphthenes, lessthan about 0.3 wt % S, less than about 0.02 wt % asphaltenes, andsubstantially free of resids other than asphaltenes, which processcomprises: adding to the synthetic crude oil a petroleum-derivednormally liquid hydrocarbon component boiling in a range from about 100°to about 1050° F., which component i) provides a greater optimum coiloutlet temperature for cracker furnace effluent than the synthetic crudeoil cracked separately.

In an embodiment of this aspect, the normally liquid hydrocarboncomponent is added to the synthetic crude oil in an amount sufficient toincrease at least one of A) cracked effluent temperature at a crackerfurnace coil outlet by about 5° to about 150° F., and B) olefin yieldresulting from cracking, as compared to the synthetic crude oil alone.

In yet another aspect, the present invention relates to a feedstock forcracking which comprises: 1) a hydroprocessed wide boiling range aliquotcontaining a) normally liquid hydrocarbon portion boiling in a rangefrom about 50° to about 800° F., substantially free of resids, and b)thermally cracked hydrocarbon liquid boiling in a range from about 600°to about 1050° F., to provide a synthetic crude oil boiling in a rangeof from about 73° to about 1077° F., containing greater than about 25 wt% aromatics, greater than about 25 wt % naphthenes, less than about 0.3wt % S, less than about 0.02 wt % asphaltenes, and substantially free ofresids other than asphaltenes; and 2) normally liquid hydrocarboncomponent boiling in a range from about 100° to about 1050° F., whichfeedstock has a greater optimum coil outlet temperature during crackingthan the synthetic crude oil alone.

In an embodiment of this aspect of the present invention, the normallyliquid hydrocarbon component is present in an amount sufficient toincrease at least one of A) cracked effluent temperature at a crackerfurnace coil outlet by about 5° to about 150° F., and B) olefin yieldresulting from cracking, as compared to that obtained using thesynthetic crude oil alone.

Embodiments of this aspect can include those wherein the normally liquidhydrocarbon component is selected from the group consisting of lightvirgin naphtha, condensate, kerosene, distillate, heavy atmospheric gasoil, virgin gas oil, hydrotreated gofinate, and hydrocrackate.Typically, the normally liquid hydrocarbon component is selected fromthe group consisting of light virgin naphtha and gas oil. Alternately,the normally liquid hydrocarbon component is selected from the groupconsisting of hydrotreated light virgin naphtha and hydrotreated gasoil.

In certain embodiments of this aspect of the present invention, thesynthetic crude oil has a pour point no greater than about 80° F.,typically no greater than about 70° F., e.g., no greater than about 52°F., say, about −12° F. while the normally liquid hydrocarbon componenthas a pour point greater than about 50° F., say, greater than about 102°F., e.g., greater than about 120° F., and the feedstock for cracking hasa pour point no greater than about 100° F., say, no greater than about64° F., e.g., no greater than about 52° F.

Embodiments of this aspect of the invention can comprise the processwherein the feedstock for cracking comprises from about 1 to about 99 wt% normally liquid hydrocarbon component and from about 1 to about 75 wt% synthetic crude oil, typically from about 75 to about 25 wt % normallyliquid hydrocarbon component and from about 75 to about 25 wt %synthetic crude oil.

In one embodiment of this aspect, the normally liquid hydrocarboncomponent is added to the synthetic crude oil in an amount sufficient toreduce the pour point of the feedstock for cracking. The pour point canbe reduced by at least about 3° F., typically at least about 5° F.,e.g., at least about 10° F.

Certain embodiments of this aspect of the invention include thosewherein the normally liquid hydrocarbon portion is a virgin refineryfeed selected from the group consisting of light virgin naphtha,condensate, kerosene, distillate, heavy atmospheric gas oil, and vacuumgas oil, and the thermally cracked hydrocarbon liquid is selected fromthe group consisting of thermally cracked very heavy crude and coker gasoil.

Other embodiments of this aspect include those wherein the normallyliquid hydrocarbon portion is a hydrotreated refinery stream selectedfrom the group consisting of gofinate and hydrocrackate, and thethermally cracked hydrocarbon liquid is selected from the groupconsisting of thermally cracked very heavy crude and coker gas oil.

In another embodiment, the normally liquid hydrocarbon portion compriseslight virgin naphtha condensate, and the thermally cracked hydrocarbonliquid comprises thermally cracked very heavy crude.

Additional embodiments of this aspect of the invention include thosewherein the synthetic crude oil contains no greater than about 0.1 wt %S, e.g., no greater than about 0.05 wt % S.

In still other embodiments of this aspect, the normally liquidhydrocarbon component is present in the feedstock for cracking in anamount sufficient to provide an optimum coil outlet temperature of thecracker furnace for the resulting mixture which is increased by at leastabout 20° F., typically at least about 50° F., e.g., at least about 70°F., over the optimum coil outlet temperature of a comparable crackerfurnace for synthetic crude oil alone.

In another embodiment of this aspect of the invention, the normallyliquid hydrocarbon component is present in the feedstock for cracking inan amount sufficient to increase the hot cracked effluent temperature atthe coil outlet of the cracker furnace to the optimum coil outlettemperature for the normally liquid hydrocarbon component. Typically,the normally liquid hydrocarbon component is present in the feedstockfor cracking in an amount sufficient to increase severity by at leastabout 0.05 C3=/C1 for each 5° F. increase in coil outlet temperature(with ratio decreasing as COT and severity is increased), e.g., in anamount sufficient to increase severity by at least 0.03 C3=/C1 for each5° F. increase in coil outlet temperature.

In still another embodiment of this aspect, the normally liquidhydrocarbon component is present in the feedstock for cracking in anamount sufficient to reduce coke make by at least about 10 wt %,typically at least about 20 wt %, e.g., at least about 35 wt %, overcoke make for the synthetic crude oil alone.

In another embodiment of this aspect of the invention, the normallyliquid hydrocarbon component is present in the feedstock for cracking inan amount sufficient to increase olefin yield from cracking by at leastabout 0.1 wt % ethylene, typically at least about 1 wt % ethylene, e.g.,at least about 2 wt % ethylene, over olefin yield for the syntheticcrude oil alone.

In certain embodiments of this aspect of the invention, the feedstockfor cracking ranges from about 0.1 to about 99 parts by weight,typically from about 1 to about 9 parts by weight, e.g., from about 1 toabout 3 parts by weight of normally liquid hydrocarbon component to eachpart by weight of synthetic crude oil.

In still other embodiments of this aspect, the wide boiling rangealiquot contains from about 0.1 to about 10 parts by weight, typicallyfrom about 2 to about 3 parts by weight of the normally liquidhydrocarbon portion for each part by weight of the thermally crackedhydrocarbon liquid.

DETAILED DESCRIPTION

The present invention provides a process for cracking a synthetic crudeoil-containing feedstock. Synthetic crude oils suitable for use in thepresent invention are prepared by i) hydroprocessing a wide boilingrange aliquot containing a) normally liquid hydrocarbon portion boilingin a range from about 50° to about 800° F., substantially free ofresids, and b) thermally cracked hydrocarbon liquid boiling in a rangefrom about 600° to about 1050° F. For purposes of the present invention,the term “normally liquid” refers to a material that is substantiallyliquid under ambient conditions, say, temperatures ranging from about32° F. to about 212° F., at about atmospheric pressure.

As used herein, non-volatile (non-distillable) components, or resids,are the fraction of a hydrocarbon feed with a nominal boiling pointabove 590° C. (1100° F.) as measured by ASTM D-6352-98 or D-2887.Non-volatiles include coke precursors, which are large, condensablemolecules that condense in the vapor, and then form coke under theoperating conditions encountered during cracking processes includinghydrocracking, catalytic cracking, thermal cracking or steam cracking.For present purposes, the term “substantially free of resids” meanscontaining less than about 70 wppm resids, preferably less than about 20wppm resids. Given the resid-based coking problems associated with usingheavier feeds in cracking processes, synthetic crude oils lacking residsare regarded with particular interest as a cracking feedstock,especially steam cracking. Asphaltenes, which may be present in resids,are n-heptane insoluble components. For present purposes, asphaltenecontent of a sample can be determined by well-known analytic techniques,e.g., ASTM D6560 (Standard Test for Determination of Asphaltenes(Heptane Insolubles) in Crude Petroleum and Petroleum Products), or ASTMD3270 (Standard Test Method for n-Heptane Insolubles).

Synthetic crude oil or “syncrude” is typically a synthetic blend ofnon-resid containing virgin liquids that have been combined withthermally cracked liquid products where the combined stream is subjectedto hydroprocessing, i.e., hydrogenating, hydrotreating, orhydrocracking. Suitable hydroprocessing conditions include a temperaturein the range of about 392° to about 896° F. (200°0 to about 480° C.),and a pressure in the range of from about 100 to about 3045 psig(690-21,000 kPa), e.g., 870 psig (6,000 kPa). The amount of hydrogenadded may be from about 500 to about 5000, e.g., 2000, standard cubicfeet (about 90-900 Nm³/m³) per barrel of feed.

Typically, the hydroprocessing is carried out under hydrotreatingconditions. Typical hydrotreating conditions vary over a wide range. Ingeneral, the overall LHSV is about 0.25 to 2.0, preferably about 0.5 to1.0. The hydrogen partial pressure is greater than about 200 psig,preferably ranging from about 500 psig to about 2000 psig. Hydrogenrecirculation rates are typically greater than 50 SCF/Bbl, and arepreferably between 1000 and 5000 SCF/Bbl. Temperatures range from about300° to about 750° F., preferably ranging from about 450° F. to about600° F. The resulting synthetic crude oil is a liquid boiling in a rangeof from about 73° to about 1070° F., containing greater than about 25 wt% aromatics, greater than about 25 wt % naphthenes, less than about 0.3wt % S, less than about 0.02 wt % asphaltenes, and substantially free ofresids other than asphaltenes.

Suitable synthetic crude oils are commercially available. Sincor crudeis a heavy non-virgin Venezuelan crude. Syncrude 319 is a heavynon-virgin Canadian crude. Both of these have been processed to providea full range crude with a gas oil endpoint. Such processing comprisesremoving heavy tail fraction by distillation, feeding the heavy tailfraction to a coker to provide a coker gas oil, blending the coker gasoil from the heavy tail with distilled bottom fraction, andhydroprocessing the resulting gas oil/bottoms blend to reduce olefinscontent. The properties of Sincor crude (Venezuelan) and Syncrude 319(Canadian) are set out below in TABLE 1.

TABLE 1 FEED PROPERTIES SynCrude 319 Sincor (Venezuela) (Canadian) Sp0.8735 0.873 Gravity 60° F. True Boiling Curve ° F. IBP 73 38 wt %  5%240 177  10% 331 271  20% 440 416  30% 512 497  40% 571 558  50% 623 610 60% 674 663  70% 730 719  80% 790 779  90% 865 851  95% 924 906 100%1052 1029

Suitable feed for admixing with the synthetic crude oil to improveoperability during cracking is a normally liquid hydrocarbon componentboiling in a range from about 100° to about 1050° F. Heavy aromatic gasoil (HAGO) is especially suited to this use in the present invention.HAGO can be obtained as a bottom side stream off an atmosphericpipestill. Properties of HAGO are set out below in TABLE 2.

TABLE 2 HEAVY AROMATIC GAS OIL PROPERTIES Specific 0.8671 GravityBoiling Curve BP (° F.) IBP 355.3 10% 554.2 20% 609.1 30% 645.8 40%668.1 50% 685.8 60% 703.5 70% 722.1 80% 744 90% 774.2 FBP 878.1

Another suitable feed for admixing with the synthetic crude oil toimprove operability during cracking is a hydrocrackate of higher pourpoint than the synthetic crude oil. Characteristics of such a high pourhydrocrackate (110° F. Pour) are set out below in TABLE 3.

TABLE 3 HIGH POUR (110° F.) HYDROCRACKATE CHARACTERISTICS Feed NameRotterdam Hydrocrackate (SOR) Feed Properties P (n-paraffins) 7.5 I(iso-paraffins) 23.8 N (napthenics) 55.3 Hydrogen content (wt %) 13.3Specific gravity 0.8674 Sulfur content (wt %) 0.004 D-86 IBP (° F.) 622D-86 BP10 (° F.) 716 D-86 IBP 30 (° F.) 769 D-86 IBP 50 (° F.) 797 D-86IBP 70 (° F.) 830 D-86 IBP 90 (° F.) 888 D-86 FBP for Gas Oils, 981 BP95 for Naphthas

In applying this invention, the hydrocarbon feedstock comprising amixture of synthetic crude oil and normally liquid hydrocarbon componentmay be initially heated by indirect contact with flue gas in a firstconvection section tube bank of the pyrolysis furnace before mixing witha dilution fluid, e.g., steam. Preferably, the temperature of the heavyhydrocarbon feedstock is from about 150° to about 260° C. (300° to 500°F.) before mixing with the dilution fluid.

Following mixing with the primary dilution steam stream, the mixturestream may be heated by indirect contact with flue gas in a firstconvection section of the pyrolysis furnace before being flashed.Preferably, the first convection section is arranged to add the primarydilution steam stream, between subsections of that section such that thehydrocarbon feedstock can be heated before mixing with the fluid and themixture stream can be further heated before being flashed.

The temperature of the flue gas entering the first convection sectiontube bank is generally less than about 815° C. (1500° F.), for example,less than about 705° C. (1300° F.), such as less than about 620° C.(1150° F.), and preferably less than about 540° C. (1000° F.).

Dilution steam may be added at any point in the process, for example, itmay be added to the hydrocarbon feedstock before or after heating, tothe mixture stream, and/or to the vapor phase. Any dilution steam streammay comprise sour steam. Any dilution steam stream may be heated orsuperheated in a convection section tube bank located anywhere withinthe convection section of the furnace, preferably in the first or secondtube bank.

The mixture stream may be at about 315° to 540° C. (600° to about 1000°F.) before introduction to the vapor/liquid separator or flashapparatus, e.g., knockout drum, and the flash pressure may be about 275to about 1375 kPa (40 to 200 psia). Following the flash, 50 to 98% ofthe mixture stream may be in the vapor phase. An additional separatorsuch as a centrifugal separator may be used to remove trace amounts ofliquid from the vapor phase. The vapor phase may be heated to above theflash temperature before entering the radiant section of the furnace,for example, to about 425° to 705° C. (800 to 1300° F.). This heatingmay occur in a convection section tube bank, preferably the tube banknearest the radiant section of the furnace.

A transfer line exchanger can be used to produce high pressure steamwhich is then preferably superheated in a convection section tube bankof the pyrolysis furnace, typically to a temperature less than about590° C. (1100° F.), for example, about 455 to about 510° C. (850° to950° F.) by indirect contact with the flue gas before the flue gasenters the convection section tube bank used for heating the heavyhydrocarbon feedstock and/or mixture stream. An intermediatedesuperheater may be used to control the temperature of the highpressure steam. The high pressure steam is preferably at a pressure ofabout 4240 kPa (600 psig) or greater and may have a pressure of about10450 to about 13900 kPa (1500 to 2000 psig). The high pressure steamsuperheater tube bank is preferably located between the first convectionsection tube bank and the tube bank used for heating the vapor phase.

The gaseous effluent from the coil outlet of the radiant section of thesteam cracker furnace can be subjected to direct quench, at a pointtypically between the furnace outlet and the separation vessel (primaryfractionator) or tar knock-out drum. Such quench can be carried out in asecondary and/or tertiary transfer line exchanger as described above.The quench is effected by contacting the effluent with a liquid quenchstream, in lieu of, or in addition to the treatment with transfer lineexchangers. Where employed in conjunction with at least one transferline exchanger, the quench liquid is preferably introduced within or ata point downstream of the transfer line exchanger(s). Suitable quenchliquids include liquid quench oil, such as those obtained by adownstream quench oil knock-out drum, pyrolysis fuel oil and water,which can be obtained from various suitable sources, e.g., condenseddilution steam.

After passage through the direct quench and/or transfer line heatexchanger(s), the cooled effluent is fed to the separation vessel (aprimary fractionator or at least one tar knock-out drum), wherein thecondensed tar is separated from the effluent stream.

The gaseous overhead of the separation vessel is directed to a recoverytrain for recovering C₂ to C₄ olefins, inter alia.

The invention is illustrated by the following Examples which areprovided for the purpose of representation and is not to be construed aslimiting the scope of the invention. Unless stated otherwise, allpercentages, parts, etc., are by weight.

EXAMPLE 1

Engineering calculations (COMPASS) which simulate processing syntheticcrude alone and admixtures of synthetic crude with HAGO in accordancewith this invention are conducted and compared with actual laboratoryresults. Reaction conditions include reactor temperature of 725° C.(measured at coil outlet), reactor pressure of about 50 kpag,steam/hydrocarbon ratio of 0.30 with severity (C3=/C1, i.e., weightratio of propylene/methane) of about 1.5 and selectivity (C2=/C1, i.e.,weight ratio of ethylene/methane) of about 1.6. Results for crackingSincor and Syncrude 319 synthetic crudes alone, or in combination withheavy aromatic gas oil (75 parts synthetic crude oil/25 parts HAGO) in acommercial size furnace as described above show an increase in ethyleneyield of about 2 wt %, reductions in radiant/quench coke make of about10 wt % and increase in optimum coil outlet temperature by about 125° F.

EXAMPLE 2

Example 1 was repeated except a high pour hydrocrackate with a pourpoint of 110° F. was substituted for the HAGO. The synthetic crudesSincor and Syncrude 319 exhibit low pour points of −12° F. Results showan increase in ethylene yield of about 2 wt %, reductions inradiant/quench coke make of about 10 wt % and increase in optimum coiloutlet temperature by about 125° F. The low pour syncrude/high pourhydrocrackate mixtures exhibit relatively low pour points of 80° F.,which makes them suitable for use without heated tanks or lines.

Although the present invention has been described in considerable detailwith reference to certain preferred embodiments, other embodiments arepossible, and will become apparent to one skilled in the art. Therefore,the spirit and scope of the appended claims should not be limited to thedescriptions of the preferred embodiments contained herein.

1. A process for cracking a synthetic crude oil-containing feedstockcomprising: i) hydroprocessing a wide boiling range aliquot containinga) normally liquid hydrocarbon portion boiling in a range from about 50°to about 800° F., substantially free of resids, and b) thermally crackedhydrocarbon liquid boiling in a range from about 600° to about 1050° F.,to provide a synthetic crude oil boiling in a range from about 73° toabout 1070° F., containing greater than about 25 wt % aromatics, greaterthan about 25 wt % naphthenes, less than about 0.3 wt % S, less thanabout 0.02 wt % asphaltenes, and substantially free of resids other thanasphaltenes; ii) adding to the synthetic crude oil a normally liquidhydrocarbon component boiling in a range from about 100° to about 1050°F.; and iii) cracking the mixture resulting from ii) in a crackerfurnace comprising a radiant coil outlet to provide a cracked effluent,wherein the cracking is carried out under conditions sufficient toeffect a radiant coil outlet temperature which is greater than theoptimum radiant coil outlet temperature for cracking the synthetic crudeoil separately.
 2. The process of claim 1, wherein the normally liquidhydrocarbon component has a greater optimum radiant coil outlettemperature than the synthetic crude oil.
 3. The process of claim 2,wherein the normally liquid hydrocarbon component is added to thesynthetic crude oil in an amount sufficient to increase at least one ofA) cracked effluent temperature at the coil outlet by from about 5° toabout 150° F., and B) olefin yields resulting from the cracking, ascompared to the synthetic crude oil alone.
 4. The process of claim 1,wherein the normally liquid hydrocarbon component is selected from thegroup consisting of light virgin naphtha, condensate, kerosene,distillate, heavy atmospheric gas oil, virgin gas oil, hydrotreatedgofinate, and hydrocrackate.
 5. The process of claim 1, wherein thenormally liquid hydrocarbon component is selected from the groupconsisting of light virgin naphtha and gas oil.
 6. The process of claim1, wherein the normally liquid hydrocarbon component is selected fromthe group consisting of hydrotreated light virgin naphtha andhydrotreated gas oil.
 7. The process of claim 1, wherein the syntheticcrude oil has a pour point no greater than about 80° F., the normallyliquid hydrocarbon component has a pour point greater than about 102°F., and the mixture resulting from ii) has a pour point no greater thanabout 100° F.
 8. The process of claim 7, wherein the synthetic crude oilhas a pour point no greater than about 52° F., the normally liquidhydrocarbon component has a pour point greater than about 120° F., andthe mixture resulting from ii) has a pour point no greater than about64° F.
 9. The process of claim 8, wherein the mixture comprises about 75wt % hydrocrackate and about 25 wt % synthetic crude oil.
 10. Theprocess of claim 1, wherein the normally liquid hydrocarbon component isadded to the synthetic crude oil in an amount sufficient to reduce thepour point of the mixture resulting from ii).
 11. The process of claim1, wherein the normally liquid hydrocarbon portion is a virgin refineryfeed selected from the group consisting of light virgin naphtha,condensate, kerosene, distillate, heavy atmospheric gas oil, and vacuumgas oil, and the thermally cracked hydrocarbon liquid is selected fromthe group consisting of thermally cracked very heavy crude and coker gasoil.
 12. The process of claim 1, wherein the normally liquid hydrocarbonportion is a hydrotreated refinery stream selected from the groupconsisting of gofinate and hydrocrackate, and the thermally crackedhydrocarbon liquid is selected from the group consisting of thermallycracked very heavy crude and coker gas oil.
 13. The process of claim 1,wherein the normally liquid hydrocarbon portion comprises light virginnaphtha condensate, and the thermally cracked hydrocarbon liquidcomprises thermally cracked very heavy crude.
 14. The process of claim1, wherein the hydroprocessing is hydrotreating.
 15. The process ofclaim 1, wherein the hydroprocessing is hydrogenating.
 16. The processof claim 1, wherein the hydroprocessing is hydrocracking.
 17. Theprocess of claim 1, wherein the synthetic crude oil contains no greaterthan about 0.1 wt % S.
 18. The process of claim 1, wherein the syntheticcrude oil contains no greater than about 0.05 wt % S.
 19. The process ofclaim 1, wherein the normally liquid hydrocarbon component is added tothe synthetic crude oil in an amount sufficient to provide an optimumcoil outlet temperature of the cracker furnace for the resulting mixturewhich is increased by at least about 70° F. over the optimum coil outlettemperature of the cracker furnace for synthetic crude oil alone. 20.The process of claim 1, wherein the normally liquid hydrocarboncomponent is added to the synthetic crude oil in an amount sufficient toincrease the hot cracked effluent temperature at the coil outlet of thecracker furnace to the optimum coil outlet temperature for the normallyliquid hydrocarbon component.
 21. The process of claim 1, wherein thenormally liquid hydrocarbon component is added to the synthetic crudeoil in an amount sufficient to increase severity by at least about 0.05C3=/C1 for each 5° F. increase in coil outlet temperature.
 22. Theprocess of claim 1, wherein the normally liquid hydrocarbon component isadded to the synthetic crude oil in an amount sufficient to increaseseverity by at least about 0.03 C3=/C1 for each 5° F. increase in coiloutlet temperature.
 23. The process of claim 1, wherein the normallyliquid hydrocarbon component is added to the synthetic crude oil in anamount sufficient to reduce coke make by at least about 10 wt %.
 24. Theprocess of claim 1, wherein the normally liquid hydrocarbon component isadded to the synthetic crude oil in an amount sufficient to increaseolefin yields from cracking by at least about 1 wt % ethylene.
 25. Theprocess of claim 24, wherein the normally liquid hydrocarbon componentis added to the synthetic crude oil to increase the optimum coil outlettemperature by at least about 70° F.
 26. The process of claim 1, whereinthe mixture resulting from adding the normally liquid hydrocarboncomponent to the synthetic crude oil ranges from about 0.1 to about 99parts by weight of normally liquid hydrocarbon to each part by weight ofsynthetic crude oil.
 27. The process of claim 26, wherein the mixtureresulting from adding the normally liquid hydrocarbon component to thesynthetic crude oil ranges from about 1 to about 3 parts by weight ofnormally liquid hydrocarbon to each part by weight of synthetic crudeoil.
 28. The process of claim 1, wherein the wide boiling range aliquotcontains from about 1 to about 10 parts by weight of the normally liquidhydrocarbon portion for each part by weight of the thermally crackedhydrocarbon liquid.
 29. The process of claim 1, wherein the wide boilingrange aliquot contains from about 2 to about 3 parts by weight of thenormally liquid hydrocarbon portion for each part by weight of thethermally cracked hydrocarbon liquid.
 30. The process of claim 1,wherein the cracking is steam cracking.
 31. The process of claim 1,wherein the synthetic crude oil is derived from shale and the normallyliquid hydrocarbon component is derived from petroleum.
 32. A processfor upgrading synthetic crude oil for cracking which synthetic crude oilis a hydroprocessed mixture of a) normally liquid hydrocarbon portionboiling in a range from about 50° to about 800° F., substantially freeof resids, and b) thermally cracked hydrocarbon liquid boiling in arange from about 600° to about 1050° F., the synthetic crude oil boilingin a range from about 73° to about 1077° F., containing greater thanabout 25 wt % aromatics, greater than about 25 wt % naphthenes, lessthan about 0.3 wt % S, less than about 0.02 wt % asphaltenes, andsubstantially free of resids other than asphaltenes, which processcomprises: adding to the synthetic crude oil a petroleum-derivednormally liquid hydrocarbon component boiling in a range from about 100°to about 1050° F., which component i) provides a greater optimum coiloutlet temperature for cracker furnace effluent than the synthetic crudeoil cracked separately.
 33. The process of claim 32, wherein thenormally liquid hydrocarbon component is added to the synthetic crudeoil in an amount sufficient to increase at least one of A) crackedeffluent temperature at a cracker furnace coil outlet by about 5° toabout 150° F., and B) olefin yield resulting from cracking, as comparedto the synthetic crude oil alone.
 34. A feedstock for cracking whichcomprises: 1) a hydroprocessed wide boiling range aliquot containing a)normally liquid hydrocarbon portion boiling in a range from about 50° toabout 800° F., substantially free of resids, and b) thermally crackedhydrocarbon liquid boiling in a range from about 600° to about 1050° F.,to provide a synthetic crude oil boiling in a range of from about 73° toabout 1077° F., containing greater than about 25 wt % aromatics, greaterthan about 25 wt % naphthenes, less than about 0.3 wt % S, less thanabout 0.02 wt % asphaltenes, and substantially free of resids other thanasphaltenes; and 2) normally liquid hydrocarbon component boiling in arange from about 100° to about 1050° F., having a greater optimum coiloutlet temperature during cracking than the synthetic crude oil alone.35. The feedstock of claim 34, wherein the normally liquid hydrocarboncomponent is present in an amount sufficient to increase at least one ofA) cracked effluent temperature at a cracker furnace coil outlet by fromabout 5° to about 150° F., and B) olefin yield resulting from cracking,as compared to that obtained using the synthetic crude oil alone. 36.The feedstock of claim 34, wherein the normally liquid hydrocarboncomponent is selected from the group consisting of light virgin naphtha,condensate, kerosene, distillate, heavy atmospheric gas oil, virgin gasoil, hydrotreated gofinate, and hydrocrackate.
 37. The feedstock ofclaim 34, wherein the normally liquid hydrocarbon component is selectedfrom the group consisting of hydrotreated light virgin naphtha andhydrotreated gas oil.
 38. The feedstock of claim 34, wherein thesynthetic crude oil has a pour point no greater than about 80° F., whilethe normally liquid hydrocarbon component has a pour point greater thanabout 102° F., and the feedstock for cracking has a pour point nogreater than about 100° F.
 39. The feedstock of claim 34, whichcomprises from about 1 to about 99 wt % normally liquid hydrocarboncomponent and from about 1 to about 99 wt % synthetic crude oil.
 40. Thefeedstock of claim 34, which comprises about 75 wt % hydrocrackate asnormally liquid hydrocarbon component and about 25 wt % synthetic crudeoil.
 41. The feedstock of claim 34, wherein the normally liquidhydrocarbon portion is a virgin refinery feed selected from the groupconsisting of light virgin naphtha, condensate, kerosene, distillate,heavy atmospheric gas oil, and vacuum gas oil, and the thermally crackedhydrocarbon liquid is selected from the group consisting of thermallycracked very heavy crude and coker gas oil.
 42. The feedstock of claim34, wherein the normally liquid hydrocarbon portion is a hydrotreatedrefinery stream selected from the group consisting of gofinate andhydrocrackate, and the thermally cracked hydrocarbon liquid is selectedfrom the group consisting of thermally cracked very heavy crude andcoker gas oil.
 43. The feedstock of claim 34, wherein the normallyliquid hydrocarbon portion comprises light virgin naphtha condensate,and the thermally cracked hydrocarbon liquid comprises thermally crackedvery heavy crude.
 44. The feedstock of claim 34, which comprises fromabout 0.1 to about 99 parts by weight of normally liquid hydrocarboncomponent to each part by weight of synthetic crude oil.
 45. Thefeedstock of claim 34, which comprises from about 1 to about 3 parts byweight of normally liquid hydrocarbon component to each part by weightof synthetic crude oil.
 46. The feedstock of claim 34, wherein the wideboiling range aliquot contains from about 0.1 to about 10 parts byweight, typically from about 2 to about 3 parts by weight of thenormally liquid hydrocarbon portion for each part by weight of thethermally cracked hydrocarbon liquid.
 47. The feedstock of claim 34,wherein the wide boiling range aliquot contains from about 2 to about 3parts by weight of the normally liquid hydrocarbon portion for each partby weight of the thermally cracked hydrocarbon liquid.